Transposition of the Great Arteries (also called transposition of the great vessels)
Transposition of the great arteries/vessels is a congenital heart defect where the two major arteries (the “great arteries” that carry blood away from the heart) arise from the wrong ventricle. The aorta is attached to the right ventricle and the pulmonary artery attached to the left ventricle, the reverse of a normal heart. This creates two parallel circulation systems that do not interact. The lungs do not oxygenate the blood; rather the blood from the body that lacks oxygen is sent through the heart and back to the body again instead of to the lungs. There is no known cause of transposition but early in fetal life the cells and tissues fail to migrate to their correct location to form the correct structures of the heart.
In order for the baby to survive, there must be some mixing of the two circulation systems, often through a ventricular or atrial septal defect (a hole between the chambers of the heart) or through a patent ductus arteriosus (the vessel found before birth that redirects some blood away from the lungs and then closes soon after birth when it is no longer needed). Prior to surgery, those other defects will be necessary for the baby’s survival.
Transposition will be diagnosed early in life because the baby’s low oxygen level causes blue-grey skin color (cyanosis), poor feeding, rapid breathing and rapid heart rate. The fetal vessel, the ductus arteriosus, usually closes soon after birth, and when it does, the cyanosis will be even more severe because there will be even less mixing of the two systems of circulation. Babies with transposition do not generally have a heart murmur, and they will quickly develop heart failure (backup of blood through the circulation because of ineffective function of the heart). Without treatment, 50% of babies will die in the first month, and 90% in the first year. Transposition occurs more frequently in mothers who are diabetic, although this risk decreases if the mother’s diabetes is carefully controlled during the pregnancy. Alcohol use during pregnancy is also associated with heart defects in the baby.
Congenital heart defects occur in 1 of every 125-150 children, so they are quite common. Of all heart defects, 5% will be transposition of the great arteries, occurring overall at a rate of 2-3 per 10,000 births. Transposition is more common in boys than girls.
Common Associated Conditions
Of children with this defect, 50% will also have a ventricular septal defect. Babies with Transposition will typically have other defects such as atrial septal defects (holes between the upper heart chambers) or patent ductus arteriosus (a small vessel between the aorta and pulmonary artery present before birth remains open after birth).
Short-term Treatment and Outcomes
An echocardiogram and cardiac catheterization will be necessary to determine the extent of the heart defect. Babies will be given the medication prostaglandin to keep the ductus arteriosus vessel open to allow blood to travel through it to the lungs to be oxygenated. Also, a balloon septostomy might be done during the cardiac catheterization procedure, which will enlarge the foramen ovale (a hole present during fetal life between the left and right upper chambers, the atria), again allowing mixing of the blood and delivering more oxygen-rich blood to the brain and body.
Although the opened ductus and foramen ovale procedure can greatly improve the baby’s condition, these are only temporary measures. During the first week of life, an arterial-switch operation will be done to move the vessels to their correct positions. The valves in these vessels will not be moved. The coronary arteries that provide oxygen-rich blood to the heart muscle do have to be removed and reconnected, however, and this is one of the most difficult parts of the procedure. However, surgical techniques have improved and this complex surgery is typically successful. The outlook for babies with transposition has greatly improved in recent years, and 95% of babies survive their arterial-switch procedure.
Long-term Treatment and Outcomes
If there is significant narrowing of the pulmonary artery, the arterial-switch surgery will not be possible and there will be difficult decisions to make regarding how to treat the baby.
Long-term, individuals with transposition will need regular follow-up with a cardiologist to detect any problems and obtain prompt treatment. Periodic echocardiograms and exercise stress tests will help determine how well the repair is functioning as the child grows.
Pulmonary hypertension is a possible complication post-operatively, as is congestive heart failure. After the arterial-switch procedure, the pulmonary artery might sometimes become increasingly narrow, causing congestive heart failure and making further surgery necessary. In rare cases, heart transplant will be an option if the other procedures are impossible and the heart and lungs are becoming increasingly damaged.
Long-term follow-up by a cardiologist is very important in order to detect and treat problems promptly. Periodic echocardiograms and exercise stress tests will be done.
Implications for Children's Development
Children’s growth can be affected if they have heart failure or lack of oxygen (hypoxia). Babies with cyanotic heart defects (lack of oxygen) can find feeding very tiring and will need to be protected from sources of infection (such as colds and pneumonia) that will also stress their heart and lungs. They may grow more slowly and have decreased exercise tolerance.
After arterial switch surgery, children usually have normal ventricular function and heart rhythms so their outlook long-term will be very good if the surgery is successful and the other vessels function well. Although they may be limited in their participation in competitive sports, they will typically not have other activity restrictions; they should, however, be allowed to self-limit their activities if they are fatigued. Parents should be encouraged to help their children to lead full, active lives and foster children’s self-confidence and independence.
For more information, including resources for parents and general information about congenital cardiac conditions, visit the following websites:
- Little Hearts
- CDC Congenital Heart Defects Information
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